Growth Inhibitory and Morphogenetic Effects of Acetone Leaf Extract of Anisomeles malabarica on the Tobacco Leaf Caterpillar Spodoptera litura (Fabricius) (Noctuidae: Lepidoptera)

Abstract

Spodoptera litura is a destructive and widely distributed insect pest responsible for considerable crop damage and substantial yield reduction. The extensive use of synthetic insecticides has adversely affected natural enemies and poses significant risks to human health and environmental safety. Consequently, botanical pesticides have emerged as potential alternatives in sustainable and organic agriculture because of their environmentally compatible characteristics and increasing consumer preference for residue-free agricultural produce. Anisomeles malabarica, an aromatic perennial herb characterised by dense pubescence, is known to possess a wide range of bioactive secondary metabolites. The present investigation evaluated the insecticidal potential of acetone leaf extract of A. malabarica against S. litura. Among the tested fractions, acetone elution 3 exhibited the highest pupal malformation (55.56%) and pupal mortality (44.44%). The same treatment produced the lowest pupal weight (0.19 g), representing a reduction of 63.40%, and the shortest pupal length (1.20 cm), representing a reduction of 21.57%. Similar observations were obtained during confirmatory screening, in which acetone elution 3 produced the lowest pupal weight (0.21 g), with a reduction of 61.11%, and the shortest pupal length (1.22 cm), with a reduction of 21.79%. Phytochemical analysis of the acetone leaf extract revealed the presence of tannins (1.32 ± 0.12) and saponins (1.11 ± 0.09), whereas flavonoids, phenols, and terpenoids were not detected. The findings of the present study indicate the potential of A. malabarica leaf extract as a botanical source for the eco-friendly management of S. litura.